RE: [EXT] Re: [PATCH V3 04/16] PCI: dwc: Perform dbi regs write lock towards the end

[Z.q. Hou]

> -----Original Message-----
> From: Jisheng Zhang [mailto:Jisheng.Zhang@xxxxxxxxxxxxx]
> Sent: 2019年4月22日 15:55
> To: Gustavo Pimentel <Gustavo.Pimentel@xxxxxxxxxxxx>; Z.q. Hou
> <zhiqiang.hou@xxxxxxx>
> Cc: Vidya Sagar <vidyas@xxxxxxxxxx>; bhelgaas@xxxxxxxxxx;
> robh+dt@xxxxxxxxxx; mark.rutland@xxxxxxx; thierry.reding@xxxxxxxxx;
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> will.deacon@xxxxxxx; lorenzo.pieralisi@xxxxxxx; jingoohan1@xxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; mmaddireddy@xxxxxxxxxx; kthota@xxxxxxxxxx;
> linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
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> Subject: [EXT] Re: [PATCH V3 04/16] PCI: dwc: Perform dbi regs write lock
> towards the end
> 
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> 
> 
> On Wed, 17 Apr 2019 09:56:33 +0000 Gustavo Pimentel wrote:
> 
> >
> > On Tue, Apr 16, 2019 at 20:27:18, Vidya Sagar <vidyas@xxxxxxxxxx> wrote:
> >
> > > Remove multiple write enable and disable sequences of dbi registers
> > > as
> > > Tegra194 implements writes to BAR-0 register (offset: 0x10)
> > > controlled by DBI write-lock enable bit thereby not allowing any
> > > further writes to BAR-0 register in config space to take place.
> > > Hence disabling write permission only towards the end.
> > >
> > > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > > ---
> > > Changes since [v2]:
> > > * None
> > >
> > > Changes since [v1]:
> > > * None
> > >
> > >  drivers/pci/controller/dwc/pcie-designware-host.c | 3 ---
> > >  1 file changed, 3 deletions(-)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > index 2a5332e5ccfa..c0334c92c1a6 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > @@ -683,7 +683,6 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
> > >       val &= 0xffff00ff;
> > >       val |= 0x00000100;
> > >       dw_pcie_writel_dbi(pci, PCI_INTERRUPT_LINE, val);
> > > -     dw_pcie_dbi_ro_wr_dis(pci);
> > >
> > >       /* Setup bus numbers */
> > >       val = dw_pcie_readl_dbi(pci, PCI_PRIMARY_BUS); @@ -723,8
> > > +722,6 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
> > >
> > >       dw_pcie_wr_own_conf(pp, PCI_BASE_ADDRESS_0, 4, 0);
> > >
> > > -     /* Enable write permission for the DBI read-only register */
> > > -     dw_pcie_dbi_ro_wr_en(pci);
> > >       /* Program correct class for RC */
> > >       dw_pcie_wr_own_conf(pp, PCI_CLASS_DEVICE, 2,
> PCI_CLASS_BRIDGE_PCI);
> > >       /* Better disable write permission right after the update */
> > > --
> > > 2.17.1
> >
> > This setup sequence was written by Jingoo Han, let's check if he did
> > this by some particular reason.
> > Jingoo do you remember why you wrote the code like this?
> 
> FWICT, enabling RO writeable in the setup sequence is introduced in commit
> d91dfe5054d4 ("PCI: dwc: Enable write permission for Class Code, Interrupt
> Pin updates"). The Reason why not towards the end maybe only enable the
> RO writeable when necessary.
> 

Yes, you get the point, I think it's not a good choice to unlock the write permission
of the RO registers all through.

Thanks,
Zhiqiang